1. Field of the Invention
This invention relates to a reformulated diesel fuel meeting the requirements of ASTM D975-96a and providing significantly reduced emissions by comparison to a certified diesel fuel, certified under Section 2282, Title 13, California Code of Regulations.
2. Description of the Related Art
Federal and state legislative bodies and agencies have issued a number of rules applicable to the production of clean diesel fuel in attempts to reduce emissions from heavy-duty vehicles of NOx, carbon monoxide, unburned hydrocarbons, and particulate matter. Diesel fuel properties given the most attention are cetane number, aromatics content, and sulfur content. Federal regulations, for instance, require vehicular diesel fuel sold beginning Oct. 1, 1993 to have a maximum sulfur content of 0.05 percent and a minimum cetane index of 40 or a maximum aromatics content of 35 percent.
Some states have issued more demanding requirements. For example, the California Air Resources Board (xe2x80x9cCARBxe2x80x9d) has adopted Section 2282, Title 13, California Code of Regulations (xe2x80x9cSection 2282xe2x80x9d) which limits the aromatic hydrocarbon content of diesel fuel sold or intended for sale as a motor vehicle fuel in California starting Oct. 1, 1993.
Section 2282 establishes a basic California statewide aromatic hydrocarbon limit for vehicular diesel fuel of 10 percent by volume with a less stringent 20 percent standard for small refiners and a temporary 20 percent standard for independent refiners.
Sections 2282(a)(1)(C) and 2282(g) allow diesel fuel producers and importers to comply with the regulation with a set of diesel fuel specifications of their choosing if they can demonstrate that the alternative specifications result in emission benefits at least equivalent to the emission benefits resulting from a 10 volume percent aromatic hydrocarbon standard (or, in the case of small refiners, the 20 percent aromatic hydrocarbon standard) reference fuel.
Section 2282(g) identifies a test procedure for comparative testing of a candidate fuel and a reference fuel representative of a diesel fuel with 10 percent aromatic hydrocarbons (or 20 percent by volume for small refiners) as specified in Section 2282(g) involving back-to-back tests using a specified heavy-duty diesel engine and identifies the statistical methodology to be used in comparing the emissions of NOx, particulate matter, and the soluble organic fraction of the particulate matter resulting from the two fuels, and establishes a process for certifying diesel fuel formulations that satisfy the regulatory criteria.
The reference fuel is defined as shown in Table I.
Exhaust emission tests using the candidate fuel and the reference fuel shall be conducted in accordance with the xe2x80x9cCalifornia Exhaust Emission Standards and Test Procedures for 1985 and Subsequent Model Heavy-Duty Diesel-Powered Engines and Vehicles,xe2x80x9d as incorporated by reference in Title 13, California Code of Regulations, Section 1956.8(b). The tests shall be performed using a Detroit Diesel Corporation. Series-60 engine, or, if the executive officer determines that the Series-60 is no longer representative of the post-1990 model year heavy-duty diesel engine fleet, another engine found by the executive officer to be representative of such engines.
Section 2282(g)(1) requires that an applicant for certification submit to the Executive Officer of CARB for approval a proposed test protocol which includes detailed information on the entity proposed to conduct the tests, the test procedures, analytical test data on the candidate and reference fuels, the quality control and quality assurance procedures, and identification of any statistical outlier tests to be used. The same section also provides procedures for applicants to submit a certification application which includes the approved test protocol, all of the test data, a copy of the complete test log, and a demonstration that the candidate fuel meets the requirements for certification.
If the Executive Officer of CARB finds that the candidate fuel has been properly tested and meets the performance criteria, an Executive Order certifying the diesel fuel formulation will be issued which assigns an identification name to the specific certified diesel fuel. The Order must specify that the certified diesel fuel formulation has the following specifications: (1) a sulfur content, a total aromatic hydrocarbon content, a polycyclic aromatic hydrocarbon content, and a nitrogen content not exceeding that of the candidate fuel; (2) a cetane number not less than that of the candidate fuel; and (3) presence of all additives that were contained in the candidate fuel in a concentration not less than in the candidate fuel, except for an additive demonstrated by the applicant to have the sole effect of increasing cetane number.
Prior to Oct. 1, 1993, many refiners in California were marketing diesel fuels which contained 35% or more aromatics. The aromatics were considered to cause a problem in the diesel fuel emissions and CARB indicated that the lower aromatics content of 10% or less was an attempt to reduce diesel fuel particulates and NOx emissions. While CARB imposed a limit of 10 volume percent, it has developed that many refiners marketed and continue to market diesel fuels which contain in excess of 20 volume percent aromatics as a result of the alternative fuel certification process. In other words, diesel fuels having an aromatics content much higher than 10 volume percent have been prepared, tested as required by CARB against the 10% aromatics reference fuel, and certified with a much higher aromatics content.
S.I.R. H1553 xe2x80x9cClean Diesel Fuel and Methods of Producing Clean Diesel Fuelxe2x80x9d, published Jul. 2, 1996 by Michael J. Pedersen, is hereby incorporated in its entirety by reference. This publication discloses a method for producing a clean diesel fuel and discloses in Example 3 the preparation of two test diesel fuels D-25 and D-26 which were prepared as described in the application, and which were subsequently certified by CARB. The certification numbers for these fuels are Executive Order G-714-007 and Executive Order G-714-008. The properties of these fuels are disclosed at column 15, at lines 6-22. The test results of the standardized combustion tests for certification are shown in Tables 3 and 4 in column 17. It will be noted that these fuels have aromatic contents of 21.7 volume percent and 24.7 volume percent, respectively.
U.S. Pat. No. 5,792,339 xe2x80x9cDiesel Fuelxe2x80x9d, issued Aug. 11, 1998 to Robert L. Russell and assigned on its face to Tosco Corporation, is hereby incorporated in its entirety by reference. This reference discloses, in Table 3 in column 4, the properties of two diesel fuels which are the subject of the claimed invention, two ARCO fuels shown as ARCO D-25 and D-26, three Chevron fuels shown as Chevron D-4781, F-2 and G-2, and one Texaco fuel. Upon observation of these fuels, it is noted that these fuels have aromatic contents varying from 15 weight percent up to 24.7 weight percent. These fuels also contain sulfur in amounts from less than 5 parts per million by weight (ppmw) up to 496 ppmw. The fuels also include polycyclic aromatics in an amount equal to from about 1.9 to about 8.6 weight percent. The nitrogen contents vary from 20 to 1050 ppmw and the minimum cetane number varies from about 50.7 up to about 59.
It will be observed that many of these fuels contain undesirable materials in relatively large quantities. For instance, most of the fuels contain quantities of aromatics well in excess of 10 volume percent. Many of the fuels also contain large amounts of sulfur and nitrogen. This serves to direct attention to the fact that the CARB regulations are directed to the requirements for a reference fuel, but there are few limitations upon the amount of polluting materials which may be contained in the candidate fuel so long as the emissions during the standardized test procedure are equivalent to or less than those generated by the reference fuel mandated by CARB. For instance, please note in U.S. Pat. No. 5,792,339, that whereas the CARB specifications for the reference fuel are shown in Table 1 and contain certain distillation requirements, the properties of the TF-1 and TF-3 fuels in Table 2 at column 3 have initial boiling points lower than permitted in the test fuel, Ten volume percent distillation temperatures lower than permitted in the test fuel, aromatics much higher than are permitted in the reference fuel, polycyclic aromatics much higher than permitted in the reference fuel, nitrogen much higher than permitted in the reference fuel and, in the TF-3, an end point higher than permitted in the test fuel. This serves to emphasize that the fuels which may be marketed under CARB certifications have little in common with the requirements for the reference fuel. As a result, it is possible to legally market fuels in California under a CARB certification, such as those shown in U.S. Pat. No. 5,792,339, which contain over 450 ppmw sulfur, over 20 weight percent aromatics, over 6 weight percent polynuclear aromatics, and as high as 1050 ppmw of nitrogen. These fuels clearly contain substantial quantities of many materials considered to be precursors to undesirable pollutants. Not surprisingly, fuels which are legally marketable under CARB regulations still result in the emission of visible and odorous pollutants from diesel-powered vehicles. This problem has been particularly pronounced in urban areas where deliveries to local retail establishments and the like via diesel-powered vehicles place the diesel-powered vehicles in close proximity to living areas, work areas and areas frequented for purposes of shopping and the like.
Recently, there has been an increased effort to eliminate or limit the use of diesel fuel in delivery trucks and other vehicles in urban areas. Not only are the exhausts from diesel engines unsightly, and in many instances odorous, they may constitute a health hazard. Accordingly, it would be desirable if a cleaner-burning diesel fuel could be developed for use in urban areas.
According to the present invention, a reformulated diesel fuel meeting the requirements of ASTM D 975-96a for a low-sulfur No. 2 diesel fuel and providing reduced emission benefits relative to a certified diesel fuel, certified under Section 2282, Title 13, California Code of Regulations, is provided. The reformulated diesel fuel contains less than 15 volume percent aromatics and has a natural cetane number of at least 55; a sulfur content less than 15 ppmw; a nitrogen content less than 10 ppmw; a polycyclic aromatics content no greater than 1.5 weight percent; at least about 14 weight percent hydrogen, and an initial boiling point of at least 350xc2x0 F. Desirably, the reformulated diesel fuel includes less than 12 volume percent aromatics and preferably less than 10 volume percent aromatics.
The reformulated diesel fuel may be produced by a process comprising charging a diesel fuel range feedstock having a boiling range from about 250 to about 790xc2x0 F (ASTM D-2887) to a hydrotreating zone with added hydrogen in the presence of a hydrotreating catalyst at conditions effective to convert at least a portion of the organo-nitrogen and organo-sulfur compounds to hydrocarbons, ammonia and hydrogen sulfide, to produce a hydrotreater effluent stream; charging at least a portion of the hydrotreater effluent stream to a hydrocracking zone with added hydrogen in the presence of a hydrocracking catalyst at conditions sufficient to produce a hydrocracking zone effluent containing a gasoline range fraction and a diesel fuel range fraction and fractionating the hydrocracking zone effluent to separate the gasoline fraction and produce the diesel fuel product. The feedstock contains aromatics in an amount and of a type such that, after processing in the hydrotreating zone and in the hydrocracking zone, the aromatics content is reduced to the desired level in the resulting diesel fuel product. Similarly, the sulfur content, polynuclear aromatics content, nitrogen content and material types are controlled in the feedstock so that after processing in the hydrotreating zone and in the hydrocracking zone, the contents of the sulfur, polynuclear aromatics and nitrogen are within the limits specified above for the reformulated diesel fuel.
The reformulated diesel fuel is useful in a method for reducing pollution resulting from the combustion of a CARB certified diesel fuel in diesel-powered ground transportation vehicles and other diesel-powered equipment by fueling such vehicles and equipment with the reformulated diesel fuel.